Telegraph exchange system



July 24, 1934. R. G. GRIFFITH TELEGRAPH EXCHANGE SYSTEM 5 Sheets-Shet l Filed May 5. 1952 INVENTOR RONALD G. GRIFFITH ATTORNEY July 24, 1934. I R GRlFFlTH 1,967,305

TELEGRAPH EXCHANGE SYSTEM Filed May 5, 1952 3 Sheets-Sheet .2

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TELEGRAPH EXCHANGE SYSTEM Filed May 5. 1932' 3 Sheets-Sheet 5 INVENTOR RONALD G. GRIFFITH ATTORNEY which circuit is also Patented July 24, 1934 STATES TENT orrlcs 1,967,305 TELEGRAPH EXCHANGE SYSTEM 1 Ronald George Grifiith, Groydon, England, as-: signer to Creed and Company, Limited, Croydon, England Application May 5, 1932, Serial No; 609,419 In Great Britain December 11, 1931 18 Claims.

l i present invention are not necessarily limited to manual exchange systemsor to exchange systems for printing telegraphs, the actual example hereinafter described has been developed primarily inview of a manual exchange system for printing telegraph communication. The presentarrangements may also be considered as an improvement of the system describediin U. S application No. 532,225 filed 23rd April 1931;

In this latter mentioned system signalling current is furnished byla source. of energy situated at the central station and means is shown whereby distinctive calling and clearing signals can be transmitted from. asubscribers station to the central station over the subscribers line circuit used for teleprinter communication.

In order to retain the advantages of the useof a polarized relay in printing telegraph receiving An apparatus in such an exchange system, which relay would be suitably biased in the case whilst single current impulses are employed for teleprinter communication, and in order to avoid the necessity for repeating relays at the central station, it has been usual to provide separate jacks or equivalent terminal connections for each subscribenone for effecting a connection to thesubscribers line circuit in response tov a calling condition. received from the subscriber and the other for eifecting a connection to the subscribers line 40 circuit in response to another subscribers request.

The object of the present invention is to provide a simplified system of connection for, a telegraph exchange system affording all the advantages of the features already outlined and in which only a single line jack or equivalent terminal connection need be provided for each subscribers line circuit. I

, Another object of the invention is toreduce the number of auxiliary circuit connections associated with a cord circuit for interconnecting any two subscribers, a single connecting wire sufficing for the communication circuit between two line jacks. i

Another object is to prov de alarm means at a v central station responsive to any one of various conditions which may have arisen to give in dication to an operator toremove the plug of a cord circuit. I

Another object of the invention is to provide an improved method of arranging for a singlebacksignalling means, at a central station to be common to a plurality of cord circuits through a plurality of operators positions.

Yet another object is to arrange so that a central station operator can plug in to a required subscribers line jack without the necessity of previously testing the busy or free condition of this subscribers station. For this purpose nieans'is provided for identifying a particular cord circuit after the operator has plugged in, if a busy? condition was encountered and no connection therefore effected by that cord" circuit.

I 'hese and other objects of the invention are attained by the arrangements hereinafter described, will be evident from the exarhplhereinafter describedin detail of the mode in' which these objects are attained, the invention consisting in thecombinations and sub-combinations more particularly defined in the appended claims.

In the drawings, Fig. l shows a diagram of connections at a subscriber's station,'Fig.2 shows the terminal connection for a subscriber at a central station and Figs. 3, 4 and 5, each figure being delimited by chain lines indicated on sheets 2 and 3, show the arrangements-and connections atthe central station, Fig. 3 showing a cord circuit, Fig. 4 an operator's position which may be common to a plurality of cord circuits, and Fig. 5 the auxiliary and like signalling apparatus which may be common to the whole central station.

It will be understood that in these drawings and for the purpose of the following description, Fig. 3, is supposed to adjoin Fig. 2. In the description also, as the various parts referred to therein are mainly located at the central station shown as a whole in Sheets 2 and 3 of the drawings, it is not thought to be necessary to refer to each individual figure for the location of detail parts.

1. A subscriber calling the exchange To call the exchange thesubscriber depresses hiscailing key CFK, thus earthing the loop and energizing his calling relay A at the exchange through the following circuit:

Earth, resistance R1 to midpoint of teleprinter relay windings, thence via both sides of theloop to contacts B3 and B4, normal, via contacts A1, normal, to the battery winding of relay A.

In operating, relay A energizes its relief relay AA via A2, operated, and locks itself in its operated condition via its earthed winding and A1, operated.

The current that traverses this circuit will be in such a direction as to hold the armature of the teleprinter polar magnet to the space side.

Relay AA in operating lights the calling lamp CL on each operators position, via B1, normal, AAB, operated, and at nighttime, if desired, sounds an audible alarm by means of relay NA, operated via B2 normal, AA4 operated.

The calling relief relayAA also prepares a locking circuit for itself at contacts AA5, operated, and prepares the Exchange answering circuit for the calling subscriber via AAl, AA2, operated, to the negative pole of the signalling battery SB and the tip connection of LJ, respectively.

2. The exchange answering the calling subscriber Observing a calling lamp CL glowing on their position, any idle operators will insert an answering plug AP of a connecting cord into the line jack LJ of the glowing calling lamp. The operator whose plug first establishes the ring connection seizes the call, and all other operators who have answered the call will receive the Bar alarm (subsequently described in paragraph 19) notifying them to withdraw.

When the operator seizes a call the out off relay B and cord relay CC are energized in series through the following circuit: v Battery, winding of relay 13 ring connections of LJ and AP, via L6 normal operating winding of relay CC to earth.

When operated relay CC energizes display pick up relay C via contacts 001 and prepares a locking circuit for itself at contacts CC2 which is completed on the operation of relay E. By the closing of contacts C03 a circuit for relay J is prepared.

In operating, relay B applies a locking potential to the winding of relay AA at B2 and extinguishes the calling lamp CL at B1. It also busies the line jack LJ (if multiplied) by applying earth potential to the sleeve connection via B5, and transfers one side of the loop from the calling relay A to the tip connection of LJ via contacts .83, AA2 operated and the other side to battery via contacts 134, AA1, operated; The operation of relay B releases relay A which restores to normal.

the Telex transmitter Motor Start relay MS at C3 and connects the impulsing relayD of the display equipment to the calling subscriber, establishing the following circuit:

Earth, contacts G2, normal, winding of relay D, contacts Cl, operated, L5, normal, tip connections of AP and LJ, contacts AA2, B3, operated, via the loop, subscribers equipment and a balancing resistance R, contacts B4, AA1, operated, via a protective resistance PR to the signalling battery SB.

The direction of current through the loop has now been reversed thus causing the armature of the teleprinter polar magnet to move to the mark side, which by tripping the crawling device, effects the automatic starting of the teleprinter motor;

The contacts of the crawling device are so arranged that contacts CD1, CD2 are closed before contacts CD3, CD4 are opened; contacts CD5, CD6 are then closed completing the motor circuit.

' This current is also of such a magnitude as to operate the subscribers indicator SI causing it to display the letters Dial. The calling subscriber is thus given indication that be can dial the number of the wanted subscriber.

Relay D in operating completes an energizing circuit for relay E at D1. Relay E when operated lights the display pilot lamp DPL and removes earth from the homing wiper W1 of the digit switch DS at and prepares a circuit for the digit switch relay F at E2.

4. The calling subscriber giving the number of the wanted subscriber In order to display the wanted number the subscriber has to transmit by means of his dial four groups of impulses which are reproduced on relay D. Relay E being slow to release holds its contacts closed during the impulsing of contacts D1.

To prevent the teleprinter polar magnet from responding to the dialling impulses a resistance R2 is shunted across the contacts DU of the dial permitting a holding current to flow through the windings of the teleprinter polar magnet to hold the armature to the mark side. This current, however, is not sufiicient to appreciably effect the impulsing of relay D. 1

The first group of dial impulses operates the first numerical switch driving magnet DMl through the following circuit:

Earth, contacts 'Dl, impulsing, contacts E2, operated, winding of relay F, via the wiper W2 and the first contact position of the digit switch DS, winding of DM1 to battery.

The first group of dial impulses, causes the wipers of the first numerical switch N51 to be stepped round to a position determined by the number dialled. The driving magnets are arranged to step the wipers round over one contact eachtime they are de-energized.

The first group of dial impulses through relay F causes it to operate and energize via contacts G1, normal contacts F1, operated, the digit switch driving magnet DMD.

At the termination of the first group of impulses, representing the first nurnber, relay D and relay E remain energized and therefore relay F is ole-energized, which in turn de-energizes the digit switch driving magnet DMD thus causing its contact wipers to be stepped on to their next contact.

At the same time the, lamp corresponding to the number dialled for the first digit is lighted via contacts G1, F1, normal, wiper W3 and second contact position of the digit switch DS, wiper W3 of the first numerical switch NSI, via the selected lamp to battery.

When the subscriber dials the second numeral, relay F is energized in series with the driving magnet DM2 of the second numerical switch NS2 via the second contact position of wiper W2 of the digit switch DS. The driving magnet DM2 is thus energized and ole-energized a. number of 1 times equivalent to the numeral dialled, stepping its wipers through a corresponding number of divisions.

At the termination of the second group of impulses relays D and E again remain energized and n la the armature of the teleprinter polar relay to' move to the mark side, which by tripping the relay Fis' again deenergized causing the driving magnet DMD to again become deenergized and step its wipers onto their third contact position; The secondnumeral isidisplayed by thefollowing circuit: Q

LContactsf G1; F1, normal, wiper W3 and the third contact position" of'DS, via wiper W3 of N52 to battery through the selected lamp. The lamp selected for the firstnumeral is now kept alight by earth being putback from wiper W2 of.NS2.,

The display of the remaining two digits is effected in an identical manner, the second and third digit lamps maintaining their earth connection via wiper W2 of N83 and N84 respectively and the fourth digit lamp, viacontacts G1,.Fl, normal, wiper W3 and the fifth contact position of the digit switch DS.

i Thus the number dialled by the calling sub-- scriberis displayed to the exchange operator.

5. The exchange operator establishing connection withthe wanted subscriber Having observed the number displayed the exchange operator inserts into the appropriate line jack LJ the calling plugCP of the connecting cord in use. The insertion of the calling plug, energizes relays H and B in series through the fol- The operationbf relay B connects the wanted subscribers equipment to the cord circuit and establishes the following circuit Earth, oontactsAA2, normaL-contacts B3, operated, via the loop, subscribers equipment, and a balancing resistance R; contacts B4, operated, AAl, normal, tip connections of LJ and CP,;contacts H3, operated, winding of supervisory relay Jfcontacts 04, normal, via a current limiting resistance R5 to signalling battery SB;

When current traverses this'current it-causes ating energizesrelay L via contacts K1.

Theoperation of relay L releases the display equipment from the cord circuit by opening the back contacts of L5 and L6. The closing of the frontcontact of L5 maintains earth on the calling subscribers loop via contacts P1, 05, N4 normal; and that of L6 completes a locking circuit for relay L via the ring connections of AP and LJ and the winding of relay B. It also completesa locking circuit for relay H at L4 and an energizing circuit'for relay M at L3. Relay Min operating accomplishes the following:

(a) Extinguishes the supervisory lamp SL by opening contacts Ml.

(b) Locks itself in its operated condition via contacts H1, M1, operated.

(c) Prepares an energizing circuit for the line cut-01f relay P at contacts M2.

(d) Prepares an energizing circuit for relay N at contacts M3.

.AA2, normal, to earth.

(e)"Pr'epares an energizing circuit for relay 0 at contacts M4. v

The first time therefore that contacts P.U.C.

are closed after the operation of relay M, pickup relay N will be energized via 03 normal, M3, operated, and when operated, will lock itself in its'operated condition via contacts N1 and the break'contacts of T.O.C. to earth.

' In this condition relay N connects the Thru transmission contacts TI of the telex transmitter, to the calling subscriber via contacts X2, S1, normal, N4, operated, resistance R4, contacts 05, P1, normal, resistance R3, contacts L5, operated, and the tip connections of AP and LJ.

6. The calling subscriber given indication that the connection has been established Teleprinter impulses are now transmitted from contacts IT via the above circuit, causing the. letters Thru to be printed on the calling sub-.-

scribers teleprinter giving him indication that connection has been established with the wanted subscriber.

7. The erchange operator given indication that the connection has been established;

Upon the operation of relay N, and therefore, during the transmission of the letters Thru, the transmission lamp TL is lighted via contacts N3;

giving the operator indication that the connection has been established and that the letters Thru are being transmitted. 8. Extending the call to the wanted subscriber The cams of the telex transmitter are so orientated that upon the completion of the transmission of the letters 'lhru, the make contacts of 'IOC of the telex transmitter are closed energizing relay 0 via N2, operated, 06, normal, M4, operated, which when operated locks itself via contacts M4, 06, M5, operated.

With the opening of the break contacts of 'I'OC the locking circuit of relay N (slow release) is opened, which restores its contacts to normal after a short period allowing sufiicient time for the operation of relay 0. I 7

Relay 0 in operating accomplishes the following: r

(a) Completes the connection together of the calling and wanted subscribers at the front contacts of O5. 7

(b) Removes the signalling battery from the wanted subscribers equipment by opening contacts O4.

(c) Completes a locking circuit for itself at 06 as mentioned above.

(d) Interrupts the operating circuit of relay N for that particular cord circuit at O3.

(e) Removes earth from the motor start relay MS at 01 which will become die-energized unless held energized by another cord circuitl Upon the extension of the call to the wanted subscriber the completedcircuit will be as follows: 7 Negative pole of signalling battery SB, protective resistance PR, contacts AAl, B4, operatedoperated, winding of supervisory relay J, contacts H3, operated, tip connections of CP and LJ, contacts AAl, normal, B l, operated, balancing resistance R via the loop and the Wanted subscribers equipment, contacts B3, operated, and

The direction of current through this circuit is such that the armatures of both teleprinter polar magnets are held to the mark side.

9. The calling subscriber verifying exchange connection After receiving indication that the connection is completed a subscriber can verify the exchange connection by depressing his Who are you key, which effects the release of mechanism in the connected teleprinter, causing it to transmit back its exchange number. Thus, having ascertained that he is connected with the desired number, the subscribed transmits his message.

10. Automatic release of the exchange display equipment from the cord circuit Upon the operation of relay L as outlined in paragraph 5, the back contacts of L5 and L6 are opened interrupting the energizing circuits of relays D and CC respectively. Relay D when deenergized, de-energizes relay E thus interrupting the locking winding of relay CC, which when deenergized opens the energizing circuit of the display pick up relay C restoring it to normal.

The display equipment is thus released from the cord circuit.

The energizing circuit of relay B is now retained via the front contact of L6 and the locking winding of relay L. Relay H is thus held energized via circuits of both the answering and calling plugs AP and CP, and therefore cannot become de-energized until both plugs have been removed. This ensures that the supervisory lamp SL will remain alight after the clearing of a connection, as will be detailed later, until both plugs have been withdrawn.

11 Resetting 0 the display equipment Relay D, when de-energized restores contacts D1 to normal, interrupting the circuit of relay E which also becomes de-energized extinguishing the display pilot lamp DPL by restoring contacts E3 to normal, and applies earth potential via the break contacts of E3 and winding of relay G to the homing wiper W1 of the digit switch DS. The driving magnet DMD is energized and upon operating opens its own contacts causing it to become de-energized and thereby rotate the wipers on to the next contact. The driving magnet contacts are new again closed and therefore the driving magnet is again energized repeating the above cycle of operations. This continues until wiper W1 reaches its normal contact where it passes the earth potential on to the homing wiper W1 of N81. This in turn homes in the same manner and places the resetting potential on to the roming wiper W1 of NS2 and so on until all the switches have reached their normal position.

During this period resetting relay G is enenergized and in its operated condition opens the circuit of impulsing relay D' at contacts G2 and removes earth potential from the display lamps i at G1.

12. The exchange operator receiving indication when connection is disengaged Having completed transmission either subscriber can clear the connection at the exchange and light the supervisory lamp SL in the following manner:

The depression of the clearing key CK for a short period de-energizes the supervisory relay J which on restoring its contactsto normal deenergizes relay K. The line cut-ofi relay P is then energized viacontacts K1, normal, M2, operated and when operated lights the supervisory lamp SL and the position pilot lamp PPL via contacts P2, P3, respectively.

- With the operation of relay P the line circuit is broken at contacts P1. These contacts will remain open until the release of relay P upon the withdrawal of both. the answering and calling plugs from their respective jacks.

13. The exchange operator breaking down connection at the exchange Observing the supervisory lamp SL and position pilot lamp PPL, glowing, the exchange operator breaks down the connection by removing both the answering and calling plugs from their respective jacks. The withdrawal of the plugs de-energizes relays H and L causing relays M, O and P also to become de-energized. and thus restore the cord circuit to its idle condition.

The de energizing of relay P extinguishes the supervisory lamp SL and the position pilot lamp PPl by opening contact P2 and P3. As explained in paragraph 10 the supervisory lamp SL will not be extinguished until both plugs have been withdrawn.

14. Antoniatic clearing. of the exchange connection To prevent a subscriber holding the line engaged indefinitely after he has concluded the transmission of his message, a crawling device CD is incorporated in the teleprinter whereby the call will be automatically cleared after an idle 15. The calling subscriber given indication that the wanted subscriber is. engaged If the exchange operator is asked for a numher that is already engaged, the insertion of the callingv plug CP into the line jack LJ will effect the printing ofthe letters Busy on the calling subscribers teleprinter in the following manner: It is arranged that no'two H relays'can operate in parallel, therefore on the insertion of CP into LJ relay R will operate due to earth potential being on the sleeve connection of the jack and contacts H2 being normal.

Relay R in operating closes an energizing circuit for the switching relay S at R4 and for relay J at R3. When operated relay S prepares a circuit for the transmission of the letters Busy at contacts S1 lights the engaged lamp EL at contacts S2 and maintains relay MS energized via contacts S3.

With the operation of relay J relays K, L, M,

N are operated and maintained in a manner rss $ i ,1 .lAn alarm has been provided on each position withdraw 'a plug from the multiple field for any' lighted via contacts N3 operated. V

The exchange operator given indication that 1 the letters fBusg have been transmitted At the conclusion of the transmission oi the letters-Busy relay 0 is energized, operated and locked in the same manner as after the transmission of the letters Thru. it interrupts the energizing circuits of relays S, J andN at contacts 01, O2, O3,- respectively. Re'lay J when de-energized, opens the energizing circuit of relay K at contacts J1, tie-energizing it. Contacts K1 are restored to normal, effecting the energizing of relay P via contacts K1, normal,

M2, operated, which when operated lights the.

. 17. The exchange operator testing for disengaged If a subscriber has more than oneline it is desirable that the operator shall be able to testall lines for Busy before notifying the calling subscriber that the number is engaged.

Anngaged test key ETK is therefore provided which when depressed interrupts the energizing circuitof the supervisory'relay J, so that if the callingplug CP is inserted into the multiple of a line jack whichis already engaged the engaged lamp EL will light on the operation of relays R and Shut the letters Busy will not be transmittedto the calling subscriber; owing to relays J, ILL,- M and N not being operated. a

r If a disengaged line is. found relay H will operate, interrupting the circuit of relay R at H2,

preventing thelighting of the engaged lampE-L and the call is extended to the wanted subscriber in the normal manner. w j

- If, however, after testing all the lines of a subscriber and finding them all, engaged, she will leavethe plug in the last jack tried and on the release of the engaged test key ETK the letters Busy will be'transmitted in the manner described in paragraph 15.

18} The exchange o'pe'rator transmitting Busy whenit is" not convenient to insert thecalling plug into aline jack If, for any reason, it is not convenient to insert the calling plug into the line'jack of a wanted subscriber, whose line or lines are engaged, the exchange operator can transmit the letters Busy :to the calling subscriberby inserting the calling plug into a special jackthat has "earth potential connected to its sleeve connection. The insertion of the plug 'will therefore effectthe transmission of the letters Busy-in an identical manner to that when a plug'isinserted into the multiple of an engaged jack. 1

19. .Bar alarm to :giveindication to an operator when she has to reason. except that of breaking down a connection at the completion of a. conversation.-

When operated These may be as follows: r I v Reason: (a) Several operators answering an incoming call.

Resume-Only displaypick-up relay C and consequently position relay E of the operator who has seized the call will'operate openingcon- "tacts El. Relay V on all other positionswill therefore be energized as follows: 1 Earth, contacts B5, operated, sleeve connections of LJ and AP, contacts Ll, E1,"U1, normal,

winding of relay V to battery.

Relay V in operating closes an energizing circuit for relay T atcontacts V2 which when operated energizes relay U by closing contacts T1 Relay U when operated locks relay T operated, via contacts U2, and breaks the energizing circuit of relay'V at U1, preparing an energizing cirI- cuit for the Bar alarm at the samecontacts. When relay V restores to normal it will close the energizing circuit for the Bar alarm'via contacts V1 normal, U1 operated,'E1, L1, normal, to earth on the sleeve connection of LJ.

The alarm will therefore sound untilthe plug is removed. j Reason:-(b Answering plug inserted into the line jack of a subscriber who has not called the exchange. 7,

Result :-The insertion of theplug will operate relays. B, CC and C.

Reason: (c) Answering plug inserted into the line jackof a subscriber who has been called. Result:0n the insertion of the plug relay CC will fail tooperate being in parallel with an H relay. 1

Reason:-(d) Calling plug inserted into a line jack of a subscriber who has just originated a 'call. u a i r Result-On the insertion of the calling plug relays H and B will be energized in series. Relay AA having been operated by the subscriber origihating the call, relay J will fall to operate due to the same potential being applied to both ends of its winding, via contacts AAl AA2 operated, contacts 04 normal. Relay V will therefore be energized via contacts H2 operated L2 normal, and the alarm will be sounded asdescribed in (a).

In this case, however, the operator will remove 20. A subscriber obtaining teleprinter connection with the exchange After having called the exchange and having been answered the subscriber by dialling the fig- .ure 0 will release a train of impulses that will effect the lighting of the lamp corresponding to O on the-thousands digit display. r l

On;observing this indication theoperator will insert the calling plug of the connecting cord in useinto the-monitors jack, extending the call to the monitors position in the normalmanner.

2 1. A subscriber clearing a call before the exchange V operator has answered Should a subscriber after-having called the ex change by depressing his calling key CFK, and before his indicator SI displays the letters .Dial, decide that hedoes not wish to complete the call, hejcan. extinguish his calling lamp. at the exchange by depressing his clearing key CK, thus interrupting the circuit of relayA, causing contacts' A1 A2. to restore to normal, breaking the energizing circuit for relay X at contacts W2,

of relays J, K, L, M, and N as described inparacircuit of relay A at A1 and of relay AA at A2. Relay AA restoringfto normal extinguishes the calling lamp CL.

22. A subscriber clearing a call due to mis -dialling Should a subscriber make a mistake whilst dialling he will depress his clearing key CK and thus mterrupt the energizing circuit of the impulsing relay D for a sufficient length of time to allow relay E to restore to normal.

Relay E when de-energized operates the Bar alarm via contacts El, L1, normal, and applies earth potential to the homing wiper W1 of the digit switch via contacts E3 normal and the winding of relay G, as explained above in paragraph llfand the switches will be returned to normal. Relay G being energized, operates and locks itself via contacts D1, E2, normal, C2, G3, operated, and removes earth potential from the impulsing relay D at contacts G2, so that the calling subscriber cannot effect the operation of this relay by further dialling.

Hearing the Bar alarm the operator will reremove the calling plug de-energizing relays B andC.

When ole-energized relay C interrupts the looking circuit of relay G at contacts C2, which when de-energized re-connects earth again to the impulsing relay D at contacts G2.

The calling subscriber can now re-call the exchange by depressing his calling key CFK as described in paragraph 1.

23. The calling subscriber given indication that the wanted subscribers line is out of order If an operator is asked for a subscriber whose line is out of order, she will insert the calling plug C Pinto the out of order jack OJ thereby efiecting the automatic transmission of the letters Faulty to the calling subscriber in the following manner.

The insertion of plug C P into jack 0 J energizes relays W and H in series, but owing to the high resistance of relay W relay H will not operate.

The operation of relay W applies earth potentialto the sleeve connections of O J and C B at contacts W1, operated, thereby completing a circuit for relay R via contacts H2 normal.

When operated relay W also completes an operated, andprepares an energizing circuit for relay Z at contacts W3, operated.

Relay X whenoperated interrupts the energizing circuit of relay S at contacts X1 operated,

prepares a circuit atv contacts X2, operated, for

the transmission of the letters Faulty from contacts FT of the telex transmitter, and. lights the out of order, lamp OL at X5. I

The operation, of relay R effects the operation graph 15, and subsequent to theope'ration of relay N the letters Faulty are automatically transmitted to the calling subscriber from. contacts FT of the telex transmitter, via contacts X2, o erateasi; normal, N4, operated, 05, P1,

via contacts N2, X3 Operated, and to relay 0 normal, L5 operated.

Upon the completion 'of'the transmission of theletters Faulty the make contacts of TOC are closed applying earth potential to' relay Z via. contacts N2, operated, 06,. normal, operated.

Relay O in perating looks itself in itsoperated condition via, contacts M5, 06, Mi, operated, and effects the subsequent operations as described in paragraph 16.

Relay Z when operated locks itself in this condition via contacts W3, Z2, operated, and interrupts the energizing circuit of relay X at contacts Z1, operated.

Relay X when de-energized restores its contacts to normal extinguishing the out of order lamp 0L, notifying the completion of the transmission of the letters Faulty.

The operator observing the supervisory and position pilot lamps glowing will remove the plugs from the jacks and so restore the cord circuit relays, and relays W and Z to normal.

24. AUTOMATIC INDICATION or FAULTS (a) Earthedlines The permanent glow of a calling lamp CL would in most cases indicate that the line connecting the subscriber with the exchange is. faulty to earth.

(b) Disconnected lines The line is automatically tested whenever the exchange operator inserts a calling plug to call a subscriber. If the line has a disconnection fault the supervisory lamp SL will glow and the number of the wanted subscriber will remain displayed, thereby giving the operator indication that the line is disconnected.

25. Indication of switching faults during connection By the lighting of the display pilot lamp DPL the exchange operator is given indication that her display equipment is connected to the calling subscriber.

If for any reason the display equipment is not seized by the calling subscriber the Bar alarm will operate. If the normal functions are not completed to establish the transmission of Thru or Busy, after the exchange operator has inserted a calling plug to complete connec tion, the Bar alarm operates.

If the switching out of the transmission of Thru or Busy is not effected indication is given to the exchange operator by the permanent glow of either the Thru or the Engaged transmission lamp.

As the switching out of the transmission of Thru or Busy is the last switching function of the cord circuit when making connection, there is no need for any further indication and the position pilot lamp covers the possibility of burnt out supervisory lamps.

26. Testing connecting cords To enable an operator to test doubtful cords before reporting them as faulty two dummy subscribers circuits terminating on two jacks DJ1 DJ2 are provided, the circuits being arranged-to represent a calling and a wanted subscriber, respectively.

To test a cord the operator will insert the answering plug into the jackv DJ1. If the plug and associated cord is satisfactory the display pilot lamp DPL will glow. Upon the inserting of the calling plug into jack DJz, if also satisfactory the lamp DPL will be extinguished and the transmission lamp TL lighted for a short period.

If either lamp fails to light then the cord will be reported as faulty.

Memo 3?. Calling subscriber requested to, re-dial the number ofthe wantedsubscriber' which is completed upon the next closure of contact'sP.U.C., thus effecting its operation. Relay Y, when operated, lights the lamp Re-Dlhvia contacts Y3 completes alocking circuit for itself from contacts T.O.C. of the telex transmitter via contacts Y2, and a transmitting circuit for the re-dialling signal from contacts Re-DT. of the telex transmitter via resistance R11, contacts Y1, operated, YYl, L. 5, normal, tip connections of AP and LJ to the callingsubscribers teleprinter. I

Upon the completion of this circuityteleprinter impulses will be transmitted from: contacts Re- D.'I'. efiecting the printing of the letters Re-dial on the calling subscribers teleprinteizf At the conclusion of the transmission, the locking winding of relay Y is interrupted by the opening of the break contacts of T.O.C. and when de energized extinguishes-lamp Re-LD.L., indicating to the exchange operator that the transmission is completed. I j

Uponthe extinction of the lamp re-D.L., the

operator will throw her position change-over key, thus connecting the subscriber to her "spare position set and causingthe subscribers indicator to display again the letters dial, informing him that he is in a position tore-dial the'number of the wanted subscriber. I II 28. Calling subscriber requested to re-call the ear- I I change An operator, upon plugging ina calling plug to call a subscriber and finding that the call is 1 not extendeddue toeither position or cord relay trouble, will request the calling subscriber to recall the exchange; I I To accomplish this, she will depress her re- 'call-key re CK for a predetermined period, ef-

fecting the energizing and operation of relay YY upon the next closureof contacts P.U.C. of the telex transmitter. When operated relay YY' lightsthe lamp re-C.L. via contacts YY5, completes a locking circuit for itself via contacts YYi,

and prepares three circuits via :co'ntacts YY1,

YY2, YY3 for the transmission of teleprinterimpulses that willeifect the printing of the letters Re-call EX. on the calling subscribens":tele- The circuit traversed by'these'impulses'will deb n n viztwhich relays have not been operated;

, Relay L not operated I Via contacts re-O'I resistance R12 contacts YYl operated, L5, normal.

2. v Relay N not. operated Via contacts re-C.'I., contacts YYZ opera ted, N4, normaLresistance R4, contacts 05, P1, normal, contacts L5,;joperated. 1

3. Relay O not. operated Contacts Re-C.T., contact, YYVB, N4 operated,

resistance R4, contacts 05, P1, normal, contacts I c c i JjIhe insertion oithe answering plug effects the 150 I L5, operated.

upon the subscriber recalling will connect him 7 through to the wanted subscriber by means of another cord, and her spare position set.

She will then test the position apparatus by means of another cord and the dummy subscriberfs jacks to ascertain whether the fault is in the position or cord circuits and will report accordingly.

29. Automatic operation of "who are you device During the establishment of a connection be- ..tween two' subscribers and coincident with the transmission of the letter U of the signal Thru the Who are you signal is transmitted to the wanted subscriber from contacts W.R.U. via contacts N5 M6, operated, 04, normal, winding of supervisory relay J, contacts H3, operated, to the Wanted subscribers equipment'via the tip connections of CP and CJ.

At the completion of the transmission of Thru the call is automatically extended as described in paragraph 8, and mechanism is released in the Wanted subscribers teleprinter, due to the transmission of the who are you signal, which eifects the transmission of its exchange number to thecalling subscriber in a manner identical to that described in paragraph 9. I The calling subscriber is therefore automatically informed that he is connected through to another subscriber and is given the exchange number of that subscriber.

30. The connection together of two subscribers connected to different exchanges To facilitate the connection together of two subscribers connected to different exchanges it can be arranged, for example on a four number display system for the thousands digit to be individual to each exchange and for the remaining three digits to beindividual to the subscribers ,lconnected to the various exchanges. a

I With this arrangement a subscriber requiring connection with a subscriber connected to another exchange will, after having called his exchange, dial the number of the wanted subscriber and thenwait until the letters Thru are printed .on his machine as detailed in the foregoing pages when connection is effected between subscribers connected to the same exchange. I

a. Exchange operator calling the distant exchange Upon receipt of the number the exchange operator will depress her trunking key T.K. which ,by closing contacts T.K.3 will hold the number displayed by applying a holdingpotential to the impulsing relay D of the display equipment.

operation of the exchange indicator at the home exchange causing it to display the letters Dial giving the exchange operator indication that she is connected to the distant exchange and can dial out the displayed number.

Still holding the trunking key depressed she will dial out by means of her dialling unit E.D.U. the number displayed on her display panel. This number will be received and displayed at the distant exchange in a manner identical to that described in paragraph 4.

With the insertion of the answering plug by the distant exchange operator relay J of the home exchange cord circuit was energized and when operated effected the operation of relays K, L, M as explained in paragraph 5.

Due to the operation of relay Q effected by the depression of the key TX. and the closure of contacts TK2, the energizing circuit of relay N was interrupted at contacts Q1 to prevent the transmission of the letters Thru on the operation of relay 0. Also by the closure of contacts Q2 an energizing circuit was prepared for relay 0 to be completed on the release of the key T.K.

c; The calling subscriber extended to the distaht exchange Having completed re-transmission of the number the exchange operator will release her key TX. and effect the energizing of relay 0 via contacts TKl, normal, Q2, operated, 06, normal, M4, operated. The opening of contacts TK2 deenergizes relay Q, but this relay being slow to release sunicient time elapses before its contacts restore to normal to allow for the operation of relay 0 and the consequent connection together of the calling subscriber and the distant exchange.

With the opening of contacts TK's relay D is ole-energized effecting the resetting to normal of the display equipment at the home exchange as described in paragraph 11.

The number of the wanted subscriber has thus been displayed at the distant exchange and the calling subscriber extended to that exchange without the transmission of the letters Thru.

d. The distant exchange operator extending the call to the wanted subscribe? The distant exchange operator having received the number of the wanted subscriber will insert the calling plug of the connecting cord in use into the appropriate jack and provided that the wanted subscriber is not engaged the call will be extended in the normal manner and the calling subscriber notified that he is connected with the wanted subscriber by the printing of the letters Thru on his teleprinter, as described in paragraph 8.

. What is claimed is: 1. In a telegraph exchange systema pluralit of subscribers stations each having a loop circuit through signalling apparatus and associated with a line jack serving for answering and calling the subscriber at a central station, a source of signalling current normally connected to both sides of each said loop circuit in parallel at the central station, means responsive to an earth condition on the loop circuit to indicate a calling condition from the subscriber, a cord circuit having an answering plug and a calling plug, means operable on plugging in said calling plug to a line jack to connect said source in series in one direction with a wanted subscribers loop, and means operable on plugging in said answering plug to a calling subscribers line jack following a calling 'cb'ndltion to connect said source in series in the other direction with the calling subscribers loop.

2. In a telegraph exchange system a plurality of cord circuits at a central station for interconnecting any two subscribers stations, a plurality of operators positions less in number than said plurality of cord circuits, back-signalling means common to said plurality of operators positions and adapted to transmit a series of code signals over a corresponding series of transmitting circuits, means individual to each cord circuit and responsive to the connection thereof to a required subscribers line circuit to effect the operation of said back-signalling means, and means at the associated said operators position responsiveto the condition of the required subscribers line circuit to complete a selective circuit from a corresponding one of the transmitting circuits of said back-signalling means to a calling subscriber through said cord circuit.

3. In a telegraph exchange system a plurality of cord circuits at a central station each cord circuit having a manually operable answering and calling plug, each plug being associated with a corresponding section of the cord circuit, backsignalling means adapted to transmit any one of a series of code signals, means responsive to the condition of a required subscribers line circuit on connecting a calling plug thereto to effect the transmission to a calling subscriber through the answering plug of a corresponding one of said series of code signals, and supervisory means individual to each cord circuit and operable on transmission of certain of said signals for identifying the cord circuit to which the said condition applied.

4. In a telegraph system, a plurality of cord circuits at a central station for interconnecting any two subscribers stations, back-signalling means adapted to transmit any one of a series of code signals, a supervisory relay individual to each cord circuit and operable on connection thereof to a required subscribers line circuit to effect the connection of said back-signalling means to a calling subscribers line circuit, other means selectively responsive to the condition of the required subscribers line circuit to effect the transmission by said back-signalling means of a corresponding one of said series of code signals to a calling subscriber, and supervisory lamp means individual to each said cord circuit and operable upon transmission of certain of said series of code signals and upon receipt of a break signal from either subscribers station notifying completion ofa call.

5. In a telegraph exchange system a plurality of cord circuits at a central station for interconnecting any two subscribers stations, back-signalling means common to said plurality of cord circuits and adapted to transmit any one of a series of code signals, a supervisory relay individual to each cord circuit and operable on connection thereof to a required subscribers line circuit to effect the connection of said back-signalling means to a calling subscribers line circuit, and other meansselectively responsive to a busy or disengaged condition respectively of the required subscribers line circuit to effect the transmission by said back-signalling means to the calling subscriber of one or other corresponding one of said series of code signals.

6. In a telegraph exchange system, a plurality of cord circuits ata central station for interconnecting any two subscribers stations, automatic back-signalling means connectible to any the transmission of certain indications such as busy or faultyand in response to a clearing condition from either of said interconnected subscribers stations notifying completion of a call. a

7. In a central station for a telegraph exchange system a plurality of cord circuits, back-signalling means common thereto, means for causing said back signalling meansto transmit any one of a series of signals over anyone of said cord circuits, and supervisorysignal means individual to eachcord circuit and selectively controlled by said back signalling means for giving an indication to an operator.

8. In a central station for a telegraph exchange system a plurality of cord circuits, back-signalling means adapted to transmit any one of a plurality of code indications, and supervisory signal means individual to each cord circuit and operable by said back-signalling means for giving an indication to an operator following transmission of certain of said plurality of code indicaitions.

9. In a telegraph exchange system a plurality of line jacks at a central station each jack serving for answering or calling a subscriber, backsignalling means, a plurality of cord circuits {each having an answering and a calling plug,

supervisory signal means individual to each cord circuit and controlled by said back-signalling means, means to render busy any said line jack, and separate bar alarm means common to said plurality of cord circuits operable on plugging a cord circuit into any said busy line jack.

10. In a control station for a telegraph exchange system a plurality of line jacks each multipled to a number of operators positions, a

;'plurality of cord circuits each having an answering and a calling plug, means to associate a busy potential with a multipled series of said line jacks, and separate bar alarm means common to said plurality of cord circuits and 5011operable on plugging either jack of a cord circuit into any of said busy series of multipled line jacks.

11. In a telegraph exchange system, a plurality of subscribers stations, a corresponding plu- ;5grality of line jacks at a central station, each jack serving to efiect an answering or a calling connection with a said subscriber, a cord circuit at the central station and having an answering and a calling plug in each half section "qgrespectively of said cord circuit, a display equipment connectible to said answering plug and operable under control of dialling impulses from a calling subscriber, selective back-signalling means operable on connection of said calling plug ;;to a required subscribers line jack, and means received over the answering half section of said ,lfplug,

13. In a telegraph exchange system, a subscribers station having a loop circuit normally without current flowing therein, a central station having a connecting means in which said loop circuit terminates, a cord circuit, and a source of energy, means responsive to the initiation-of a call by said subscribers station for causing said source of energy to supplycurrent in a normal direction to said loop circuit, means res onsive to the interconnection of said cord circuit with said connecting means for causing said source of energy to supply current in the opposite direction to said loop circuit, and a printer at said subscribers station adapted to be held'inoperative when no current is flowing in the loop circuit and when the current flow in said loop circuit is in saidnormal direction and to be rendered operative when the current flow therein is in the opposite direction.

14.111 a telegraph exchange system, a subscribers station having a loop circuit normally Without current flowing therein, a central station having a connecting means in which said loop circuit terminates, a cord circuit having an answering plug, and a source of energy, means responsive to the initiation of a call by said subscribers station for causing said source of energy to supply current in a normal direction to said loop circuit, means responsive to the interconnec tion of said answering plug and said connecting means for causing said source of energy to supply current in the opposite direction to said loop circuit, and a printer at said subscribers station adapted to be held inoperative when the current flow in said loop circuit is in said normal irection and to be rendered operative when the current flow therein is in the opposite direction.

15. In a telegraph exchange system, a subscribers station having a loop circuit normally without current flowing therein, a printer and a l polarized relay included in said loop circuit and adapted to hold said printer inoperative when the current flow in the loop circuit is in a normal direction but to render it operative when the current flow therein is in the opposite direction, a central station having a connecting means in which said loop circuit terminates, a cord circuit, and a source of energy, means responsive to the initiation of a call by said subscribers station for causing said source of energy to supply current in a normal direction to said loop circuit, and means responsive to the interconnection of said cord circuit with said connecting means for causing said source of energy to supply current in the opposite direction to said loop circuit.

16. In a telegraph exchange system, a plurality of subscribers stations each having a loop circuit normally without current flowing therein, a central station having a plurality of line jacks in each of which a loop circuit terminates, a plurality of cord circuits and a single source of potential, means responsive to the initiation of a call by a subscribers station for causing said source of energy to supply current in a normal direction to the calling subscribers loop circuit, means responsive to the interconnection of a cord circuit with the calling subscribers line jack for causing said energy source to supply current in the opposite direction to the calling subscribers loop circuit, and a printer at each subscribers station adapted to be held inoperative when the current flow in the subscribers loop circuit is in the normal direction and to be rendered operative when the current flow therein is in the opposite direction.

ice?

17. In a telegraph exchange system, a subscribers station having a loop circuit normally without current flowing therein, a central station having a line jack in which said loop circuit terminates, a cord circuit, and a source of energy, relay means associated with said line jack and responsive to the initiation of a call by the subscribers station for causing said source of energy to supply current in a normal direction to said. loop circuit, said relay means being also responsive to the connection of said cord circuit and said line jack to cause said source of energy to supply current in the opposite direction, and a printer at said subscribers station adapted to be held inoperative when the current flow in said loop circuit is in the normal direction and to be rendered operative when the current flow is in the opposite direction.

18. In a telegraph exchange system, a subscribers station having a loop circuit normally without current flowing therein, a central station having a line jack in which said loop circuit terminates, a cord circuit, a source of energy, a first means, responsive to the initiation of a call by said subscribers station, for causing said source of energy to supply current in a normal direction to said loop circuit, and a second means responsive to the connection of said cord circuit to said line jack when answering and calling said subscribers station, for causing said source of energy to supply current in the opposite direction to said loop circuit, and a printer at said subscribers station adapted to be held inoperative when the direction of current flow in said loop circuit is in the normal direction and to be rendered operative when the current flow therein is in the opposite direction.

RONALD GEORGE GRIFFITH. 

